A conventional apparatus for driving a service function unit of a multi-function telephone set comprises a key operation unit including dial keys of 0 to 9 and at least one function key, a controlling unit such as a microprocessor, and a memory.
In operation, when a plurality of keys which are in a predetermined order including the function key are pushed in the key operation unit to supply key information to the controlling unit, the controlling unit decodes the key information to drive the service function unit to operate a corresponding function. For instance, when the dial key "9" is pushed twice and then the function key "SEND" is pushed to produce key information "9, 9, SEND", the controlling unit decodes the key information to identify as information of a shortened dial call, so that a certain phone number, which is registered beforehand at a corresponding address of a registering area in the memory of the telephone set, is called up. On the other hand, when the function key "FNC" is pushed and then the dial key "1" is pushed twice to produce key information "FNC, 1, 1", the controlling unit decodes the key information to identify as information of a calling time displaying function, and the time is displayed. Other functions are instructed to be carried out in the similar key operation as explained above.
According to the conventional apparatus for driving a service function unit of a multi-function telephone set, however, there is a disadvantage in that predetermined keys must be pushed in order, for instance, three times to instruct the service functions, because the number of keys which can be disposed on a limited area of the front panel of the telephone set is limited. As a result, a user of the telephone set may be reluctant to use such a service function.